In the field of printed wiring boards, permanent mask resists (protective films) have conventionally been formed on printed wiring boards. In steps of flip-chip mounting of semiconductor elements on printed wiring boards using solder, permanent mask resists serve the role of preventing adhesion of solder onto undesired sections of the conductive layer of the printed wiring board. Permanent mask resists also serve the role of preventing corrosion of the conductive layer and of maintaining the electrical insulating properties between conductive layers, during use of the printed wiring board.
In the prior art, permanent mask resists for printed wiring board production are manufactured by, for example, methods of screen printing of thermosetting or photosensitive resin compositions.
For example, in flexible wiring boards employing such mounting systems as FC, TAB and COF, a thermosetting resin paste is screen printed on areas except for the rigid wiring board, IC chip, electronic part or LCD panel and connection wiring pattern sections, and then the thermosetting resin paste is thermoset to form a permanent mask resist (see Patent document 1, for example).
Also, in semiconductor package boards such as BGA (ball grid arrays) or CSP (chip-size packages), that are loaded in personal computers, it is necessary to remove the joined sections of the permanent mask resist: (1) for flip-chip mounting of the semiconductor element on the semiconductor package board via solder, (2) for wire bonding joints between the semiconductor element and semiconductor package board, and (3) for solder joining of the semiconductor package board on a motherboard substrate, and the permanent mask resists used have been photosensitive resin compositions which facilitate such removal (see Patent document 2, for example).